Hope this is the correct forum because, hopefully, this can only be a fantasy (or rather, your worst nightmare).
YOU MUST KILL HUMANS IN ORDER TO SAVE THE PLANET
You and a bunch of others have been abducted by a violent alien race. In their spaceship they take you to planets where life exists, and they make you
watch as they blow up these planets. You quickly come to understand that their technology is way beyond anything we humans have.
One ugly, purple, alien informs all of the abductees that it is the alien belief that all life has no right to exist, except their own species. It is
their prime directive to travel the universe and kill, kill, kill. However, they do enjoy toying with other life forms, so you are offered a way to
save planet earth. You will be returned to earth where each of the abductees must kill one human per month. All it takes is for one of you to not
comply and the whole planet gets immediately obliterated.
There are about thirty abductees. You will have microscopic cameras implanted in your brain so that the aliens can watch you kill. While your camera
is being implanted, the alien performing this procedure whispers to you that not all of them want to destroy life, and if you can hold on for as long
possible - if you can kill a few in order to save the many - there will be an alien uprising to put a stop to all this death.
Is this alien lying to you? Giving you false hope to ensure that you will kill in order to save the planet (to ensure that you will kill for their
viewing pleasure)? You just don't know.
The only thing you are certain of is that earth will definitely explode if you DON'T kill.
So, the question is, will you do it?
How will you kill so that you don't get caught? Getting caught means you will be incarcerated and no longer able to kill - and the planet goes boom!
How do you inform the human powers that be so they can work on a way to destroy the aliens, knowing that you'd probably just get locked up for life
as a lunatic - and the planet goes boom!
Is there any way out of this that you can see?
Note: I love coming up with ideas that keep my mind occupied for hours at a time. I hope you enjoy this one as much I will.